Ceramic superconductive powder

Abstract

A superconductive oxide powder is produced by a method comprising spray drying a slip to form agglomerates, feeding the agglomerates sequentially through a first and a second oxygen supported combustion flame for fusing the fine particles in the agglomerates to form an intermediate powder, annealing the intermediate powder in an oxygen-containing environment such as to produce a friable mass, and crushing the mass to form the superconductive oxide powder. For example, a precursor compound in the slip is barrium carbonate, the other precursor constituents are yttrium oxide and copper oxide, and the yttrium, barium and copper in atomic proportions in the precursor constituents are 1:2:3+Y where Y denotes a copper surplus having a value of up to about 1.5. In the final powder the proportions are 1:2:3+Z where Z is between about 0.2 and 1.0.

What is claimed is: 
     
       1. A powder useful for producing superconductive coatings by thermal spraying, comprising an oxide defined by the formula R a  T b  Cu c  O d  or R a  T b  Cu c  O d  X c , where H is at least one element selected from the group consisting of yttrium, ytterbium, neodymium, samarium, europium, gadolinium, holmium, erbium, dysprosium, lanthanum, lutecium and thulium, T is barium with 0 to 7 at % of an additional metal, the at % being based on the total of the barium and the additional metal and the addition metal being selected from the group consisting of sodium, potassium, rubidium, cesium and combinations thereof, Cu is copper, O is oxygen, X is fluorine, sulfur or a combination thereof, a and b are nominally 1 and 2 respectively, c is between about 3.2 and 4.0, the total of d and known as "1-2-3". The "X" denotes a small oxygen deficiency, and e is between about 6.5 and 7, and e is up to 0.3; wherein the powder is produced by a method comprising the steps of forming a slip containing a spray dry binder and fine particles of at least one precursor constituent selected for forming a superconductive oxide, spray drying the slip to form spray dried agglomerates of the fine particles, feeding the spray dried agglomerates through a first oxygen supported combustion flame having sufficient heat content for alloying the fine particles in the spray dried agglomerates to form an intermediate powder annealing the intermediate powder in an oxygen-containing environment such as to produce a friable mass of material, and crushing the friable mass to form the powder.   
     
     
       2. A powder according to claim 1 wherein, according to the method, the combustion flame has sufficient heat content to fuse the fine particles in the spray dried agglomerates. 
     
     
       3. A powder according to claim 1 wherein, according to the method, the combustion flame is surrounded with oxygen shroud gas. 
     
     
       4. A powder according to claim 1 wherein the intermediate powder comprises intermediate particles of spheroidal shape, and the step of crushing the friable mass is effected sufficiently gently to form the powder as powder particles having substantially the spheroidal shape. 
     
     
       5. A powder according to claim 1 wherein the method further comprises the step of feeding the intermediate powder through a second oxygen supported combustion flame having sufficient heat content for further alloying the intermediate powder. 
     
     
       6. A powder according to claim 5 wherein the powder comprises at least one cation component of a superconductive oxide, the at least one precursor constituent includes a heat-decomposable compound of the cation component with a non-oxygen component, the first combustion flame has sufficient heat content and sufficient oxygen content for at least partially decomposing the compound and for at least partially oxidizing the cation component in the intermediate powder and for removing a portion of the non-oxygen component from the intermediate powder, and the second combustion flame has sufficient heat content and sufficient oxygen content for removing a further portion of the non-oxygen component from the intermediate powder. 
     
     
       7. A powder according to claim 1 wherein the powder comprises at least one cation component of a superconductive oxide, the precursor constituent includes a heat-decomposable compound of the cation component with a non-oxygen component, and the combustion flame has sufficient heat content and sufficient oxygen content for at least partially decomposing the compound, and for forming an oxide of the cation component in the intermediate powder and for removing at least a portion of the non-oxygen component from the intermediate powder. 
     
     
       8. A powder according to claim 7 wherein the compound is a carbonate with the non-oxygen component being carbon. 
     
     
       9. A powder according to claim 8 wherein the carbonate is barium carbonate. 
     
     
       10. A powder according to claim 1 wherein the slip is formed with a plurality of precursor constituents. 
     
     
       11. A powder according to claim 10 wherein the powder comprises preselected proportions of a plurality of cation components of a superconductive oxide and the precursor constituents comprise corresponding precursor compounds of the cations components, at least one cation component bein susceptible to a measurable loss in proportion relative to the cation components resulting from the feeding of the spray dried agglomerates through the combustion flame, and the method further comprises an initial step of selecting proportions of the precursor constituents with a equal to the measurable loss whereby the powder is formed of the preselected proportions. 
     
     
       12. A powder according to claim 1 wherein the oxide is defined by the formula R a  T b  Cu c  O d  where R is yttrium and T is barium. 
     
     
       13. A powder useful for producing superconductive coatings by thermal spraying, comprising an oxide defined by the formula R a  T b  Cu c  O d  or R a  T b  Cu c  O d  X e , where H is at least one element selected from the group consisting of yttrium, ytterbium, neodymium, samarium, europium, gadolinium, holmium, erbium, dysprosium, lanthanum, lutecium and thulium, T is barium with 0 to 7 at % of an additional metal, the at % being based on the total of the barium and the additional metal and the addition metal being selected from the group consisting of sodium, potassium, rubidium, cesium and combinations thereof, Cu is copper, O is oxygen, X is fluorine, sulfur or a combination thereof, a and b are nominally 1 and 2 respectively, c is between about 3.2 and 4.0, the total of d and e is between about 6.5 and 7, and e is up to 0.3. 
     
     
       14. A powder according to claim 13 wherein the oxide is defined by the formula R a  T b  Cu c  O d  where R is yttrium and T is barium.